Mechanical classifier

ABSTRACT

A mechanical classifier for separating sludge into coarse grained and fine-grained portions, and having a trough with a bottom ascending at a slant above which a conveying mechanism is disposed for advancing the coarse-grained material upwardly along the trough bottom. A weir for overflow of the fine-grained material is located at the deep end of the trough, and a sludge inlet is provided above the level of the weir for introducing the sludge into the trough. Supplementary water is applied to the trough between the sludge inlet and the discharge end of the trough bottom through at least one conduit which extends transversely over the trough bottom and upwardly of the two sidewalls of the trough above the level of the sludge bath established by the weir. The conduit includes a protective shield facing the sludge inlet and ascending at a slant toward the trough axis. Supplementary water supplied to the conduit passes therefrom through openings below the bath level preferably formed as slits in the conduit wall facing toward the discharge end of the trough. To increase the separating capability of the classifier, additional conduits may be provided, preferably arranged in spaced transverse zones to permit sedimentation of the materials between the zones.

Unit States Patent 1 Web. 29, 1972 Weiss [54] MECHANICAL CLASSIFIER [72]Inventor: Viktor Weiss, Radenthein, Austria [73] Assignee:Osterreichisch-Ameriltanische Magnesit Aktiengesellshatt [22] Filed:Nov. 18, 1969 [21] Appl. No.: 877,613

[30] Foreign Application Priority Data Nov. 20, 1968 Austria ..A11275/68 [52] 11.8. CI ..209/464, 209/500 [51] "8031 3/32 [58] Field ofSearch ..209/464, 500, 461, 463, 18,

[56] References Cited UNITED STATES PATENTS 1,984,362 12/1934 Dickson..209/464 2,353,152 7/1944 Erck ....209/464 X 2,368,416 1/1945l-lolt.... ....209/464 X 1,972,195 9/1934 Lacy ..209/463 2,373,6624/1945 Dickson.. ....209/464 X 2,428,789 10/1947 Dickson ..209/464 XPrimary Examiner-Tim R. Miles Assistant Examiner-Ralph J. HillAttorneyl-lowson and l-lowson [5 7] ABSTRACT A mechanical classifier forseparating sludge into coarse grained and fine-grained portions, andhaving a trough with a bottom ascending at a slant above which aconveying mechanism is disposed for advancing the coarse-grainedmaterial upwardly along the trough bottom. A weir for overflow of thefine-grained material is located at the deep end of the trough, and asludge inlet is provided above the level of the weir for introducing thesludge into the trough. Supplementary water is applied to the troughbetween the sludge inlet and the discharge end of the trough bottomthrough at least one conduit which extends transversely over the troughbottom and upwardly of the two sidewalls of the trough above the levelof the sludge bath established by the weir. The conduit includes aprotective shield facing the sludge inlet and ascending at a slanttoward the trough axis. Supplementary water supplied to the conduitpasses therefrom through openings below the bath level preferably formedas slits in the conduit wall facing toward the discharge end of thetrough. To increase the separating capability of the classifier,additional conduits may be provided, preferably arranged in spacedtransverse zones to permit sedimentation of the materials between thezones.

8 Claims, 5 Drawing Figures PATENTEUFEB 29 I972 INVENTOR. VI KTOR W E lSS BY k ATTORNEYS MECHANICAL CLASSIFIER The invention concerns amechanical classifier having the purpose of separating a sludge into acoarse-grained sediment and a portion containing the fine-grainedmaterial, and having a trough with a bottom that ascends at a slant,over which is disposed a conveying mechanism for pushing forward thesediment, having an inlet for the sludge, having an overflow for theportion which contains the fine-grained material, and having a dischargefor the sediment which is conveyed by the conveying mechanism to thehigher end of the trough bottom, and equipped with a contrivance forsupplying supplementary water to the sludge.

Depending on the type of classifier, the conveying mechanism is a rakingband or a scraping band, a conveyor worm, or the like. Thecoarse-grained sediment is brought out of the sludge upon the bottom ofthe slanting upward trough, and is conveyed to the discharge. Theportion of the sludge which contains the fine-grained material isallowed to flow away at the lower end of the trough, through theoverflow, which is usually made as a weir.

The classifying effect of mechanical classifiers is based on theprinciple of equal settling by gravitation. Grains having more than acertain sinking speed sink to the bottom, and this sunk material orsediment is conveyed by the conveying mechanism to the discharge. Thefine grains (mud) which have a slower sinking speed flow along with thesludge off by way of the overflow.

For various reasons the sought for separation by means of equal settlingtakes place only imperfectly, and with an inaccurate separation, becauseon the one hand a part of the sludge becomes discharged along with thesunk material or sand, and on the other hand a part of thecoarse-grained material gets into the overflow. These imperfect outputsmust be ascribed chiefly to the so-called impeded settling of thegranular material, a phenomenon which begins to occur with a more thanabout percent content of solid materials in the sludge. Additionalcauses for the imperfect outputs are the clinging of the finer particles(adhering grains) to the larger grains, and agglomerates of fine grainsbeing carried along by the coarse grains into the sediment.

The supplementary water supplied flows when introduced into the sludgethrough the layer of material which has been pushed forward between thetrough bottom and conveyor mechanism toward the discharge and whichconsists of coarsegrained sunk material, and the water is intended tofree the fine grains, or agglomerates of them, from the coarse grainswhich enclose them or to which they cling, and to drive them up into thepart of the sludge flowing toward the overflow, for the purpose ofdecreasing the erroneous portion of finegrained material in the sunkmaterial or sediment carried off to the discharge, thus improving theseparating sharpness of the classifier.

For this purpose, in the case of the known classifiers, thesupplementary water is brought in through a plurality of openings whichare distributed and constructed, between the sludge inflow and the zonesituated at the discharge end of the sludge bath, in such a way that thesupplementary water enters into the sludge over the entire zone in asuniform a distribution as possible. Hereby for example there can beinstalled in the trough a sieve plate set parallel to the trough bottom,above which sieve plate there runs a conveyor device provided withscrapers. The supplementary water enters from the sides, at a number ofuniformly spaced places, into the space of the trough below the sieveplate, and flows in uniform distribution through the sieve holes intothe sludge.

In the case of another known form of construction there is likewise asieve above the trough bottom. in this case the supplementary water isconducted into the intermediate space situated between the trough bottomand the sieve, and it emerges from there out of tubes set transverselyof the trough, and having in them numerous openings arranged in such away that the emerging supplementary water becomes divided up fanwise,for the purpose of entering, after it has passed through the sieve, asuniformly as possible into the sludge.

As a result of the arrangement and distribution of the openings in thecase of the classifiers referred to in the foregoing and in the case ofother classifiers, the numerous closely adjacent openings in thelongitudinal and transverse directions of the trough produce in a largeregion a more or less uniform ascending current flow. Through this thesludge in the said region is set into general turbulence, which does infact promote the loosening of fine grains from the sunk material, butwhich however at the same time greatly hinders the settling of thegrains by equal settling. Furthermore, as a result of the greatturbulence of the sludge in this region, fine material out of the upperpart of the sludge sinks downward into the sunk material or sediment,and coarse grains become driven upward out of this sediment into theupper part of the sludge, through which the sharpness of separation ofthe classifier becomes impaired and the parting line between fine andcoarse grain will tend to the coarse grain.

The invention has the purpose of constructing a mechanical classifier ofthe kind described at the outset, in such a way that the sludge by meansof the supplementary water supplied becomes set into turbulence in asfew as possible separate upward flow zones, which suffice for an asextensive as possible removal-loosening of the fine-grained particlesout of the sunlt material or sediment, and for the transfer of thesefine-grained particles into the part of the sludge flowing toward theover flow, but which however does not disturb the unobstructed settlingof the grains over a great region of the sludge. By this means it ispossible to decrease the proportion of fine grains in the sunk materialand to increase it in the overflow.

In accordance with the invention this objective is attained in that,with a mechanical classifier of the described kind, there is disposed inthe region between the sludge inflow and the discharge end of the sludgebath and at the inside of the trough at least one conduit for supplyingthe supplementary water, which extends over the trough bottomtransversely of the longitudinal direction of the trough and at bothsidewalls of the trough upward to above the surface level of the bath,and which is provided with openings for the outflow of the supplementarywater. Preferably the conduit has, at its end turned toward the sludgeinlet, a protective shield ascending at a slant from the inside of thetrough toward its longitudinal middle axis, and supported at its freerim, at its end toward the discharge, against the inside of the trough,and it is, in its wall turned toward the discharge, and in the region ofit below the surface level of the sludge bath, provided with openingspreferably slit shaped, for the emergence of the supplementary water.

This form of construction of the mechanical classifier according to theinvention offers many significant advantages, which include theelimination of openings in the trough walls, the permissible connectionof the conduit to a supply pipe of water under pressure without boringthrough the trough walls, and the use of an upward slanting protectiveshield which can be made from a suitable strong and rigid material,through which wear from the friction of the sedimentary material can bekept very small. With the openings for the emergence of thesupplementary water made slit shaped, and with their disposal in thewall of the conduit at the discharge end of the conduit, an entry offine grains into the conduit is prevented or is at least made minimal,and wear or damage of the edges of the openings is scarcely to befeared.

In accordance with a further characteristic of the invention there aredisposed in the trough at least two conduits parallel to one another ina transverse zone, their spacing apart being relatively small, and beingpreferably only a little greater than the width of the protective shieldmeasured in the lengthwise direction of the trough. When use is made oftwo conduits disposed in this way, through the upward flowing turbulenceproduced in this region, there is generally produced a substantialincrease in the separating sharpness of the classifier.

If it is desired to increase the separating sharpness of the classifierto a particularly great degree, in accordance with a furthercharacteristic of the invention there may be disposed,

in another transverse zone adjoining a transverse zone having twoconduits, another conduit for the supply of supplementary water, wherebyits spacing or the spacing of its openings from the openings of theneighboring conduit of the first transverse zone must be great enoughfor a zone of as undisturbed sedimentation as possible to be leftbetween them. This spacing in general amounts to a multiple, for exampleat least quadruple, of the spacing of the openings in the conduits ofthe said first transverse zone as measured in the lengthwise directionof the trough. With this arrangement of the conduits there is producedin the sludge, beyond the first upward flow turbulence zone which isformed by one or two conduits a further turbulence zone. In practicallyalmost all cases this suffices to liberate from the sunk material orsediment the final residues of any fine-grained material that may stillbe contained in it.

From the construction point of view, the conduits can be made verysimply. In accordance with one form of construction their wall turnedtoward the sludge inlet is formed of the protective shield risingslantingly inside the trough, and the wall turned toward the dischargeend of the trough consists of a support wall connected to the free rimof the protective shield and to the inside of the trough, in which aremade openings, slit openings in particular, for the emergence of thesupplementary water. In accordance with another form of construction theconduit consists of a tube which at its end turned toward the sludgeinlet is connected to the free rim of the protective shield, and whichat the part of the tube wall turned toward the discharge end of thetrough is provided with openings for the emergence of the supplementarywater.

In accordance with one particularly advantageous further development ofthe mechanical classifier of the invention through the conduit orthrough each conduit there is passed a flexible hose, made for exampleof rubber or of synthetic material which extends out of the upper rimsof the conduit and to which there can be connected a supply line ofwater under pressure, and has a plurality of slits disposed in the hosewall for the emergence of the supplementary water. The slit openings inthe hose are advantageously made in the form of cuts made in thelengthwise direction into the hose, which have a self-closing actionsimilar to that of check valves, preventing entry of sludge into thehose. By means of the protective shield and of the other parts of thewall the hose is well protected against wear or damage, and, if need be,it can, after the supply of water under pressure is shut off, be pulledin a simple manner out of the conduit, and after this conduit has beengiven the washing out that is needed if desired it can be replaced byanother hose.

The hose or hoses are advantageously connected at each end in turn to asupply line of water under pressure, through which the pressuregradient, which would exist with connection at one end only, issubstantially eliminated.

Each connection line of the pressurized water supply is advantageouslyprovided with its separate regulating valve, for the purpose of makingit possible to regulate in each conduit the quantity of supplementarywater supplied and its pressure, in a suitable manner.

With one particularly advantageous form of construction of theclassifiers of the invention all conduits are mounted on a commonsupporting metal sheet that can be inserted to fit into the trough,whereby if desired the tubes supplying water under pressure are mountedwith their connection pipes on connectors that can be fastened to theupper part of the trough sidewalls or to the support sheet for theconduits. In the case of this form of construction the entirearrangement for supplying the supplementary water can be made in a formthat corresponds to the size and shape of the trough and ready to beinstalled in that trough, and, after removal of the conveyor worm or ofthe raking or scraping band, it can be inserted into the trough, afterwhich, when the conveying mechanism has been put back, the classifier isready for operation.

Interchanging or replacing the hoses can be considerably facilitated andsimplified if each hose is at both its ends attachable, by means ofordinary hose clips, to hose nozzles,

which can be connected by means of detachable hose couplings to theconnection tubes of the pipes supplying'the water under pressure. Bythese means the time needed to replace a hose can be shortened to suchan extent that the operation of the classifier does not need to beinterrupted at all, the only thing necessary being to interrupt the flowof water to the hose concerned.

For the purpose of preventing contact of the conveyor mechanism with thewalls of the conduits, but however to ensure an effective pushingforward of the sediment in the unobstructed region of the trough, in thecase of a classifier according to the invention the spacing between theouter rim of the material-driving element of the conveyor mechanism andthe inner surface of the trough in the region of the conduits can bemade greater than the spacing between these two parts in theunobstructed part of the trough by an amount corresponding to the radialheight of the conduits. In the case of conveyor worms this can be donethrough a suitable milling off of the rim part of the worm blade, or inthe case of conveyors having raking or scraping bands by means oflaterally disposed rollers or slide rails in the region of the conduits.

The invention will be explained in more detail in the following withreference to the forms of construction illustrated in the drawing.

Referring to the drawings, FIG. I shows in longitudinal section amechanical classifier according to the invention equipped with aconveyor worm;

FIG. 2 shows a plan view of the classifier of FIG. 1;

FIG. 3 is a sectional view taken along line IIIlII of FIG. 1;

FIG. 4 is a sectional view taken along line IV-IV of FIG. 2; and

FIG. 5 is a view similar to FIG. 4 showing a modified form of theinvention.

Referring to the drawings and particularly the embodiment of theinvention shown in FIGS. 1 to 4, the mechanical classifier has a troughhaving an upward slanting bottom 1, above which is disposed the conveyormechanism, in the form of a conveyor worm 2, which in the case of theexample of construction is mounted rotatably in two bearings 3 and 4,and which is driven in the direction of the arrow r through theintermediary of a belt drive 5 from a reduction gear 6, whereby thereduction gear drive 6 is in its turn driven by a belt drive 7, drivenfor example by an electromotor 8.

The trough has near its lower end a weir formed of a partition 9, whoseupper edge 10 determines the surface level 11 of the sludge, whichtogether with the fine-grained material it contains flows over thepartition to an outlet 12. In the one sidewall 13 of the trough there isprovided an inflow 14 for the sludge, and at the higher end of thetrough is disposed a discharge 15 for the coarse-grained sedimentconveyed to this upper end by the conveyor worm 2.

In the trough there are disposed on the trough bottom 1 conduits, whichin the illustrated example of construction are three conduits 16, 17,18, provided with openings 24. In the present case these conduits arenot fastened to the trough wall itself, but are mounted on a commonsupporting metal sheet 19 which is inserted into the trough. The spacingbetween the openings 24 of the two conduits l6 and 17 is relativelysmall,

in proportion to the trough length that is, whereas the spacing of theopenings of the third conduit 18 from those adjacent conduit 17 issubstantially greater than, and at least four times as great as that ofthe spacing between the openings of the two conduits 16 and 17. In thedrawing, for reasons of clarity, the spacing between the openings of theconduits l6 and 17 is shown greater than actuality.

Each conduit runs transversely of the longitudinal axis A- A of thetrough, above the trough bottom 1, and extends upward, at the inner faceof the two sidewalls 13, 20 of the trough, to above the surface level 11of the sludge.

Each conduit has, at its side turned toward the inflow 14 for thesludge, a protective shield 21, which slants upward toward the troughaxis from its edge connected to the support sheet 19 or the trough wall.The conduit can hereby be made in different ways. In FIG. 5, the conduitconsists of a tube 25, which is provided with numerous outlet openings24 in the form of elongated slits, for the supplementary water, alongthe tube axis, and it is connected at its side turned toward the sludgeinlet M to the protective shield 21. In the modified example shown inFIG. 4 the protective shield '21 itself forms the wall of the conduit 16and I7 respectively turned toward the sludge inlet M, and at the sideturned toward the discharge the wall of the conduit consists of asupport wall 23, connected to the free rim 22 of the protective shield2I and to the support sheet 19 or the trough bottom 1, and in which aremade numerous slitlike openings 24 for the emergence of thesupplementary water and disposed below the surface level II of thesludge.

In the preferred example of the invention, the conduits 16, 17, I8, 25have flexible hoses 26, made for example of rubber or of syntheticmaterial, run through them, these hoses being provided with a series ofcut-in slits 27 for the emergence of the supplementary water, they beingself-closing similar to check valves, so as to permit an outflow ofwater from the hose, while preventing an entry of sludge into the hose.

As can be seen from FIG. 3, at each end 28 where it emerges from theassociated conduit, the hose 26 is for example by means of a commercialclip 29 fastened to a hose nozzle 30, which in its turn can by means ofa suitable screwthreaded hose coupling 31 be connected to a connector 34of a pipe 35 supplying water under pressure and equipped with aregulatory valve 32 and a pressure gauge 33, inside which pipesupplementary water under pressure greater than the counter pressureexerted by the sludge is supplied in the direction of the arrow winFIGS. I and 2.

When the conduits are mounted on a common support sheet 19, the pressurewater pipes 35, together with their connecting pipes 34, canadvantageously be mounted on supports 36, which can be fastened to theupper part of the trough side walls or to the common support plate 19 ofthe conduits. In this case the complete arrangement for the supply ofsupplementary water can be combined into a unit ready to install, whichafter removal of the conveyor worm or of some other conveyingarrangement from the trough can be inserted into the said trough.

In the region of the conduits, for the purpose of keeping the spacing ofthe edge of the drive element of the conveying mechanism, for examplethe outer rim 37 of the conveyor worm 2, away from the contour of theconduits by a distance as great as that separating the worm from thetrough bottom in the clear space of the trough, in the case of aconveyor worm its outer rim in the region of the conduits can bemachined off as indicated by the schematic profile line 38 of FIG. 1,where the conveyor worm is shown of uniform diameter along its entirelength.

The invention is not limited to the illustrated and described form ofconstruction, and its design may be modified within the scope of theinvention as defined in and limited solely by the appended claims.

Iclaim:

l. A mechanical classifier for the separation of a sludge into acoarse-grained sediment and a portion containing the finegrainedmaterial, comprising a trough having an inclined bottom, a conveyormechanism in said trough for moving the sediment upwardly along saidinclined trough bottom, a weir at the lower end of said inclined troughbottom for overflow of the fine-grained material, discharge means insaid trough adjacent the upper end of said inclined trough bottom abovethe level of said weir, an inlet for the sludge adapted to introduce thesludge into said trough intermediate said weir and the discharge end ofsaid trough, said conveying mechanism being adapted to move the sedimenttoward and into said discharge means, and means for conductingsupplementary water into the sludge, the improvement wherein said meansfor conducting supplementary water into the sludge comprises at leastone conduit in the region between the sludge inlet and the discharge endof the trou h bottom, said conduit extending transversely over the troubottom and upwardly at the two sidewalls of the trough to above the weirlevel, said conduit having at its side turned toward the sludge inlet aprotective shield which ascends at a slant from the inside of the troughtoward its longitudinal middle axis, said conduit including a wallturned toward the trough discharge end having openings therein in theregion situated below the weir level for the emergence of thesupplementary water.

2. A mechanical classifier in accordance with claim I, characterized inthat there are disposed in the trough, in a first transverse zone, atleast two conduits which run parallel to one another, and whose spacingapart from one another is small relatively to the trough length, and ispreferably only a little greater than the width of the protective shieldmeasured in the lengthwise direction of the trough.

3. A mechanical classifier in accordance with claim 2, characterized inthat at the discharge side and adjoining said first transverse zonehaving at least two conduits, at least one additional conduit isdisposed in another transverse zone for supplying supplementary water,whereby the spacing of its openings from the openings of the adjacentconduit in the first transverse zone is at least four times as great asthe spacing of the openings of the two conduits of the first transversezone from one another.

4. A mechanical classifier in accordance with claim 2, characterized inthat all the conduits are mounted on a common supporting metal sheetwhich can be inserted into the trough, whereby if desired the pipessupplying water under pressure are mounted by connector pipes onsupports which can be fastened to the upper part of the "troughsidewalls or advantageously to the supporting metal sheet of theconduits.

5. A mechanical classifier in accordance with claim I, characterized inthat each wall of a conduit turned toward the sludge inlet is formed ofthe protective shield sloping up from the trough inside, and the conduitwall turned toward the discharge end of the trough consist of a supportwall connected to the free rim of the protective shield and to thetrough inside, and in this wall are made openings for the emergence ofthe supplementary water.

6. A mechanical classifier in accordance with claim 5, characterized inthat the conduit consists of a tube which at its side turned toward theinlet for the sludge is connected to the free edge of the protectiveshield, and is at its part turned toward the discharge end of the troughprovided in its tube wall with openings for the emergence of thesupplementary water.

7. A mechanical classifier in accordance with claim 1, characterized inthat through the conduit or through each conduit is run a flexible hose,made for example of rubber or of synthetic material, which extends outof the upper rims of the conduit and can be connected to a pipesupplying supplementary water under pressure, and is provided with aplurality of slits disposed in the hose wall, for the emergence of thesupplementary water.

8. A mechanical classifier in accordance with claim 1, characterized inthat the conduit is connected at both its ends to a pipe which suppliessupplementary water under pressure.

1. A mechanical classifier for the separation of a sludge into acoarse-grained sediment and a portion containing the fine-grainedmaterial, comprising a trough having an inclined bottom, a conveyormechanism in said trough for moving the sediment upwardly along saidinclined trough bottom, a weir at the lower end of said inclined troughbottom for overflow of the finegrained material, discharge means in saidtrough adjacent the upper end of said inclined trough bottom above thelevel of said weir, an inlet for the sludge adapted to introduce thesludge into said trough intermediate said weir and the discharge end ofsaid trough, said conveying mechanism being adapted to move the sedimenttoward and into said discharge means, and means for conductingsupplementary water into the sludge, the improvement wherein said meansfor conducting supplementary water into the sludge comprises at leastone conduit in the region between the sludge inlet and the discharge endof the trough bottom, said conduit extending transversely over thetrough bottom and upwardly at the two sidewalls of the trough to abovethe weir level, said conduit having at its side turned toward the sludgeinlet a protective shield which ascends at a slant from the inside ofthe trough toward its longitudinal middle axis, said conduit including awall turned toward the trough discharge end having openings therein inthe region situated below the weir level for the emergence of thesupplementary water.
 2. A mechanical classifier in accordance with claim1, characterized in that there are disposed in the trough, in a firsttransverse zone, at least two conduits which run parallel to oneanother, and whose spacing apart from one another is small relatively totHe trough length, and is preferably only a little greater than thewidth of the protective shield measured in the lengthwise direction ofthe trough.
 3. A mechanical classifier in accordance with claim 2,characterized in that at the discharge side and adjoining said firsttransverse zone having at least two conduits, at least one additionalconduit is disposed in another transverse zone for supplyingsupplementary water, whereby the spacing of its openings from theopenings of the adjacent conduit in the first transverse zone is atleast four times as great as the spacing of the openings of the twoconduits of the first transverse zone from one another.
 4. A mechanicalclassifier in accordance with claim 2, characterized in that all theconduits are mounted on a common supporting metal sheet which can beinserted into the trough, whereby if desired the pipes supplying waterunder pressure are mounted by connector pipes on supports which can befastened to the upper part of the trough sidewalls or advantageously tothe supporting metal sheet of the conduits.
 5. A mechanical classifierin accordance with claim 1, characterized in that each wall of a conduitturned toward the sludge inlet is formed of the protective shieldsloping up from the trough inside, and the conduit wall turned towardthe discharge end of the trough consist of a support wall connected tothe free rim of the protective shield and to the trough inside, and inthis wall are made openings for the emergence of the supplementarywater.
 6. A mechanical classifier in accordance with claim 5,characterized in that the conduit consists of a tube which at its sideturned toward the inlet for the sludge is connected to the free edge ofthe protective shield, and is at its part turned toward the dischargeend of the trough provided in its tube wall with openings for theemergence of the supplementary water.
 7. A mechanical classifier inaccordance with claim 1, characterized in that through the conduit orthrough each conduit is run a flexible hose, made for example of rubberor of synthetic material, which extends out of the upper rims of theconduit and can be connected to a pipe supplying supplementary waterunder pressure, and is provided with a plurality of slits disposed inthe hose wall, for the emergence of the supplementary water.
 8. Amechanical classifier in accordance with claim 1, characterized in thatthe conduit is connected at both its ends to a pipe which suppliessupplementary water under pressure.